When sharing data visualizations (i.e., interactive visual representations of data) online, a user may wish to annotate these data visualizations to communicate with other users more effectively. Text-based annotation of documents is well established and considerable research has been performed concerning the annotation of online web pages in general. However, these systems typically only offer text-based annotations of a webpage; thus not offering a way to include user drawn graphics within the annotations.
Since data visualizations are often inherently graphical, text-based annotations may be cumbersome and may only allow for a limited range of expression. While a limited number of systems allow for free form annotations on media, these systems may not allow for the reuse of annotations within different contexts.